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"Morse Code" interference on speakers?


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Back when I had AT&T and T-Mobile phones, I would often get a morse-code like interference on speakers near my phone (especially my unshielded computer speakers and my car stereo). When I switched to Sprint three phones ago that problem went away. I assumed that it was a GSM-only issue.

 

Now, for the past few days, my EVO 4G LTE has been causing the same interference on my car speakers. It sounds like the exact same "dit-dit-dit" pattern. Could this be because LTE is based on GSM? Or maybe it is an 800Mhz issue? Anyone else experienced this?

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Back when I had AT&T and T-Mobile phones, I would often get a morse-code like interference on speakers near my phone (especially my unshielded computer speakers and my car stereo). When I switched to Sprint three phones ago that problem went away. I assumed that it was a GSM-only issue.

 

Now, for the past few days, my EVO 4G LTE has been causing the same interference on my car speakers. It sounds like the exact same "dit-dit-dit" pattern. Could this be because LTE is based on GSM? Or maybe it is an 800Mhz issue? Anyone else experienced this?

 

I've had that issue when I had T-Mobile as well. I had always assumed it was because the phone was GSM too because Sprint's and Verizon's frequency's (1900mhz & 800mhz) never caused that kind of interference.

 

If I had to take a guess I'd say it's happening to you again because LTE is similar to GSM, but who knows? Personally, I enjoyed it when I T-Mobile phone because I could put my phone on silent and the speakers would just make that noise whenever I got a text message. No one else where I worked had no idea that I was texting lol. Also for client meetings we have over head projectors with speakers on them. Well I would always know when someone wasn't paying attention because the speakers would freak out all meeting long.

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From what I've seen, "GSM buzz" only happens on 850MHz TDMA-based systems...so TDMA, iDEN and GSM. CDMA-based systems don't do that. Nor do 1900MHz ones...I've had T-Mobile and never run across GSM buzz while on their home network (1900MHz for GSM, AWS for HSPA+ in most areas, with a few now having HSPA+ on PCS). I have seen the buzz, or something similar to it, on TDMA, GSM and iDEN phones before, all of which were in the 800MHz (SMR or CLR) band at the time.

 

LTE should NOT be making that kind of interference pattern, and I haven't seen it on my SIII when it has been in LTE mode. Once LTE is online where I am (or where I'm visiting) I'll do some tests, but LTE's airlink is closer to WiMAX or WiFi than GSM, CDMA or even WCDMA/HSPA.

 

I repeat, just because LTE is a 3GPP standard doesn't mean it's similar to GSM...it isn't. At all. Just like WCDMA (AT&T and T-Mobile 3G/non-LTE 4G) behaves completely differently than GSM (which is why you don't hear GSM buzz nearly as much anymore, since WCDMA doesn't do it).

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When I had Nextel I used to have interference on unshielded speakers. Could be because EVO LTE can use 800 MHz channel that was iDEN (Nextel) before. When you get interference next time go to DEBUG screen on ur EVO LTE then go to 1X engineering RF and let us know what channel and Band class ur phone is using at that time.

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Okay, I'm officially an idiot. I installed a Progressive Insurance "Snapshot" device in my car last week, and it just occurred to me that it must be using a cellular connection to report my driving stats. A quick web search later, and sure enough, Snapshot uses AT&T. Mystery solved!

 

EDIT: A little further research shows that the buzz comes from the amplifier power control cycle in TDMA GSM, in which the cellular radio starts broadcasting pulses at max power to initiate communication with the tower. These pulses can cause the amplifier to draw at least 2 amps in 217Hz pulses, so the Snapshot, which is getting power from my car, is probably introducing the noise directly into my car's power system.

 

We now return you to your regularly scheduled CDMA and FDMA discussions.

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Guys, RF frequency (e.g. 800 MHz, 850 MHz, 1900 MHz) is not the issue. The cause of the audible speaker interference is TDMA burst frequency. GSM is most notable in this regard, as its TDMA burst frequency is 216.67 Hz for full rate, 108.33 Hz for half rate -- both of which are well within the audible range of 20 Hz - 20 kHz. In other words, a traffic state GSM mobile transmits powerful RF bursts a few hundred times per second, and unshielded electronics may reproduce the frequency of these bursts as an audible buzz.

 

AJ

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Ain't no way in the world I am going to report my driving habits to my insurance company. Otherwise they would be able to assess my risk more appropriately. I count on hiding behind the risk curve! :hah:

 

Robert

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Ain't no way in the world I am going to report my driving habits to my insurance company. Otherwise they would be able to assess my risk more appropriately. I count on hiding behind the risk curve! :hah:

 

Robert

 

Ditto. You will not find such a unit in my vehicle, but on the open road you would find a radar detector.

 

I do have a cheap ODB2 unit for use with the Torque diagnostic app on my Android, but I don't keep it plugged in all the time. There's too much battery drain when the app is in operation.

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What's the snapshot thing do? Plug in your obd2 port and record the sensors like speed and acceleration? Then send it to them for a lower rate?

 

Yep, a friend of mine did/does it. Apparently he was able to get a dirt cheap rate, because he "drove like an old grandma" in the words of his insurance agent. The FAQ is here: http://www.progressive.com/auto/snapshot-common-questions.aspx

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What's the snapshot thing do? Plug in your obd2 port and record the sensors like speed and acceleration? Then send it to them for a lower rate?

 

It measures the total distance you drive, the times of day you drive, and how hard you brake. Technically it is just recording your VIN and speed from the OBDII, getting time from the cellular modem, and using an accelerometer to make sure you aren't feeding it bogus data from an OBD emulator. There's no GPS or any way of telling your location (unless they triangulate with the AT&T towers, but they say they don't).

 

You get dinged for hard braking over 7MPH/s, driving during moderate risk times (9PM-9AM and 4PM-6PM), driving during high risk times (12AM-4AM), and driving over 30mi/day. They don't care if you're speeding, since they have no way of knowing what road you're on and what the speed limit is. At least in Massachusetts your rate can't go up because of Snapshot, and your discount is up to 30%.

 

In my case, my work hours are flexible so I can avoid moderate and high risk times, my commute is 20 miles round trip, and I am careful enough about keeping a large following distance so that I haven't had to do any hard braking. If I need to make a long trip or drive late at night I'm usually with someone else who can drive until my 3 months are up.

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it all comes down to part 15 of the fcc rules. the cell phone is a transmitter and when a device, say a pair of amplified computer speakers is near, it will act as a receiver and sometimes you'll hear the phones handshake to the tower. when i have my phone next to my laptop and my headphones are plugged in i can hear the handshake and know when a call or text message is coming in before the phone even alerts me.

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when i have my phone next to my laptop and my headphones are plugged in i can hear the handshake and know when a call or text message is coming in before the phone even alerts me.

 

Ya that used to happen to me! When I had a work Nextel phone I could always tell I had an incommimg call before the phone rang by the "dit...dit...dit" on the computer speakers.

 

KCT - "No Matter Where You Go, There You Are!"

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it all comes down to part 15 of the fcc rules. the cell phone is a transmitter and when a device, say a pair of amplified computer speakers is near, it will act as a receiver and sometimes you'll hear the phones handshake to the tower. when i have my phone next to my laptop and my headphones are plugged in i can hear the handshake and know when a call or text message is coming in before the phone even alerts me.

 

What does Part 15 have to do with this other than stating a P15 device cannot cause interference, and has to be able to accept or reject outside interference?

Edited by kf2m
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What does Part 15 have to do with this other than stating a P15 device cannot cause interference, and has to be able to accept or reject outside interference?

 

you'll have to live with the radio in the car picking up the interference. unless you can re locate the snapshot device or put some ferrite chokes on the input power wires and antenna in connector.

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